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PubMed2005

Selective involvement of opioids in the mechanisms of synapse-specific plasticity in the common snail during the acquisition of sensitization.

Studies on defensive behavior command neurons LP11 and RP11 in semi-intact common snail preparations were performed to investigate the effects of the opioid peptide met-enkephalin and the opioid antagonist naloxone on the effects of nociceptive sensitization. Application of nociceptive stimuli to the snail's head elicited marked reversible membrane depolarization along with depression of neuron responses to sensory stimulation during the short-term stage of sensitization and facilitation of responses in the long-term stage. Met-enkephalin at a dose of 10 microM but not at a dose of 0.1 microM partially suppressed responses to nociceptive stimuli. Acquisition of sensitization during exposure to met-enkephalin at doses of 10 and 0.1 microM led to complete suppression of the facilitation of responses to tactile stimulation of the head. Facilitation of responses to chemical stimulation of the head and tactile stimulation of the foot in these conditions was similar to that of neurons in control sensitized animals. Acquisition of sensitization during exposure to met-enkephalin and/or naloxone elicited selective suppression of facilitation of responses to chemical stimulation of the head but had no effect on facilitation of responses to tactile stimulation of the head and foot. Met-enkephalin and naloxone had no effect on the depression of neuron responses evoked by sensory stimulation in the short-term stage of sensitization. It is suggested that during the acquisition of sensitization in the common snail, opioids are involved in controlling the mechanism of nociception and in the mechanisms of selective induction of long-term plasticity of the synaptic inputs to command neurons activated by tactile and chemical stimulation of the animal's head.

Analgesics, Non-Narcotic↗

PubMed2005

Inositol triphosphate and ryanodine receptors in the control of the cholinosensitivity of common snail neurons by the Na,K pump during habituation.

The effects of the Na,K pump inhibitor ouabain on habituation of the common snail to tactile stimulation were identical to the ouabain-induced modification of the decrease in the cholinosensitivity of defensive behavior command neurons in the common snail in a cellular model of habituation. Studies addressed the effects of intracellularly delivered ligands of two types of Ca2+ depot receptors--inositol triphosphate (IP3) receptors and ryanodine receptors--on the action of ouabain in the cellular analog of habituation. The IP3 receptor antagonist heparin (0.1 mM), the IP3 receptor agonist inositol triphosphate (0.1 mM), and the ryanodine-dependent Ca2+ mobilization inhibitor dantrolene (0.1 mM) prevented ouabain from modifying the depression of the evoked acetylcholine current. The ryanodine agonist/antagonist ryanodine was used at two concentrations (0.1 and 1 mM) and neither had any effect on the action of ouabain. It is concluded that Ca2+ mobilized from intracellular Ca2+ depots via IP3 receptors is involved in the neuronal mechanism of regulation of the habitation of the common snail to tactile stimulation by the Na,K pump.

Acetylcholine↗

PubMed2006

Methiothepin-sensitive serotonin receptors are involved in the postsynaptic mechanism of sensitization of the defensive response in the common snail.

Rhythmic electrical stimulation of the snail foot leads to sensitization of the defensive reflex. This sensitization has dynamics similar to those of posttetanic potentiation of the amplitude of the acetylcholine-evoked influx current of defensive behavior command neurons in the common snail. It is likely that an increase in the cholinosensitivity of the somatic membrane of defensive behavior command neurons in the common snail may be involved in the mechanism of sensitization of the animal's defensive response. Methiothepin, an antagonist of serotonin receptors, prevented the posttetanic potentiation of the acetylcholine-evoked influx current as well as behavioral sensitization. Serotonin, like methiothepin, also impaired posttetanic potentiation of the acetylcholine-evoked influx current. It is suggested that methiothepin-sensitive serotonin receptors are involved in the postsynaptic mechanism of behavioral sensitization.

Acetylcholine↗

PubMed2006

Comparative studies of the effects of chlorpromazine and 5,6-dihydroxytryptamine on locomotion, defensive reactions in the snail Helix lucorum, and command neuron excitability in long-term sensitization.

The actions of the neuroleptic chlorpromazine (CPZ) and the neurotoxin 5,6-dihydroxytryptamine (5,6-DHT) on defensive reactions, locomotion, formation of long-term sensitization, and the electrical characteristics of command neurons in the common snail were compared. Prolonged (chronic) treatment with CPZ led to a significant increase in the pneumostoma closure time, as well as changes in motor behavior, with a decrease in the rate of locomotion. Administration of 5,6-DHT in small daily doses for one week was accompanied by gradual decreases in the rate of locomotion of the snails, which persisted for one week. A similar effect was seen after administration of the same total dose of neurotoxin, 30 mg/kg, as a single injection. Administration of CPZ prevented the formation of long-term sensitization, as did treatment with 5,6-DHT. The procedures of treatment with CPZ, long-term sensitization, long-term sensitization followed by CPZ, and acquisition of long-term sensitization on the background of treatment with CPZ gave a locomotion speed which was directly proportional to the length of the sole. No such relationship was seen during the acquisition of long-term sensitization on the background of treatment with 5,6-DHT. Electrophysiological studies showed that chronic CPZ led to a depolarization shift in the membrane potential and a decreased action potential generation threshold in command neurons, which also occurred on treatment with 5,6-DHT. It is concluded that the actions of the neuroleptic CPZ on defensive behavior and locomotion in the common snail, as well as on the electrical characteristics of identified neurons, were similar to the toxic actions of serotonin.

5,6-Dihydroxytryptamine↗

PubMed1989

The spread of freshwater snails including those of medical and veterinary importance.

The present paper discusses the spread of freshwater snails that act as intermediate hosts for various trematodes that cause diseases in man and in cattle. Examples of snail species which have spread across natural barriers are reviewed as well as the mechanisms involved in this transport. Focus is put on the extensive trade in freshwater aquatic plants and aquarium fish, and the need for better control of this trade is emphasized in order to minimize the risk of unintended import of potentially harmful snails.

Animals↗

PubMed1986

Autoradiographic evidence for receptor cell renewal in the olfactory epithelium of a snail.

The tentacles of the terrestrial snail Achatina fulica contain an epithelium at their tips which is specialized for olfaction. The histology of the snail's olfactory organ bears a striking resemblance to that of the olfactory mucosa in the nose of vertebrates, where the receptor cell population is known to undergo a continuous process of renewal. In the present experiments, [3H]thymidine was delivered as a single pulse that was determined to have a maximum duration of about 1 h. Thirty minutes after an injection of [3H]thymidine, presumptive precursor cells were found labeled within, or at the edges of, receptor cell lobules. At later survival times, label was seen over cells that were identified as receptors. The mean position of the labeled cells within the layer of receptor cells became progressively more superficial with increasing survival times, indicating an upward migration of newly differentiated cells. The labeling index in the snail is ca. 0.7%, compared to 0.9% in the mouse. The turnover time is about 45 days, compared to 30-45 days in the mouse.

Animals↗

PubMed1987

Effect of 5,7-dihydroxytryptamine on the food-aversive conditioning in the snail Helix lucorum L.

The effects of 5,7-dihydroxytryptamine (5,7-DHT), a drug which selectively ablates serotonergic terminals, were examined on acquisition of food-aversive conditioned reflex in the snail Helix lucorum. The percent of feeding reactions decreased from 80 to 15% in the conditioned group of animals after 5-8 pairings of food and electric shock. The behavioral performance of 5,7-DHT-injected animals after the same training session coincided with the data received from the unpaired control group: the percent of feeding reactions remained the same as before the training. Conditioning was carried out on the semi-intact 'lip-CNS' preparations as well. Intracellular recordings from the neurons responding to the withdrawal reaction confirmed the results of the behavioral experiments. Elaboration of associative changes was effective on preparations made from normal snails, whereas no changes were noted in 5,7-DHT-treated and pseudoconditioned animals. In 5,7-DHT-treated animals some components of the feeding behavior and withdrawal reaction changed as well. The appetitive phase duration of feeding lengthened significantly, moreover the sensitization of the withdrawal reaction evoked by rhythmic tactile stimulation disappeared in preparations made from drug-treated snails.

5,7-Dihydroxytryptamine↗

PubMed1990

Day-night rhythms in the inhibitory effects of 60 Hz magnetic fields on opiate-mediated 'analgesic' behaviors of the land snail, Cepaea nemoralis.

There is accumulating evidence that magnetic fields can affect a variety of opioid-mediated behavioral and physiological functions. The present experiments were designed to examine the effects of various durations of day- and night-time exposures to low intensity (1.0 gauss rms) 60 Hz magnetic fields on light (L) and dark (D) period opioid-mediated aversive thermal ('nociceptive') responses and morphine-induced 'analgesia' in the nocturnally-crepuscularly active land snail, Cepaea nemoralis. The snails displayed a LD rhythm in the latency of their aversive (40 degrees C) thermal (nociceptive) responses, showing a significantly greater response latency at night than during the day. Administration of morphine (10 mg/kg/2.0 microliters) elicited significant increases in the thermal response latencies indicative of the induction of analgesia. The snails displayed a significantly greater analgesic response at night than during the day. Exposure (0.50, 2, 12, 48 or 120 h in L or D) to the 60 Hz fields reduced morphine-induced analgesia in both the L and D periods, with the magnetic stimuli having significantly greater inhibitory effects in the D period. The magnetic fields also significantly attenuated the level of the dark period basal nociceptive response latencies, while not affecting the light period responses. In both the L and D periods the degree of attenuation of the analgesic and nociceptive response latencies was related to the duration of exposure to the 60 Hz magnetic fields.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesia↗

PubMed1991

Evidence for the involvement of protein kinase C in the modulation of morphine-induced 'analgesia' and the inhibitory effects of exposure to 60-Hz magnetic fields in the snail, Cepaea nemoralis.

There is substantial evidence that magnetic fields can reduce opiate-induced analgesia, with alterations in calcium channel function and/or calcium ion flux being implicated in the mediation of these inhibitory effects. The present experiments were designed to examine the effects of protein kinase C (PKC), a calcium/diacylglycerol/phospholipid-dependent protein kinase, on opiate-induced analgesia and its involvement in mediating the inhibitory effects of exposure to magnetic fields. We observed that morphine-induced antinociception, or 'analgesia', in the land snail, Cepaea nemoralis, as measured by the enhanced latency of response to a thermal (38.5 degrees C) stimulus, was reduced in dose-related manner by the PKC activator, SC-9. Exposure of snails for 2 h to a low intensity (1.0 gauss rms) 60-Hz magnetic field also reduced morphine-induced analgesia. The inhibitory effects of the 60-Hz magnetic field on morphine-induced analgesia were significantly reduced by the PKC inhibitors, H-7 and H-9, and significantly enhanced by the PKC activator, SC-9. The non-specific protein kinase inhibitor, HA-1004, and the preferential calmodulin inhibitor, W-7, had no significant effects on either morphine-induced analgesia or the inhibitory actions of exposure to the magnetic fields. These results suggest that: (1) PKC has antagonistic effects on opiate-mediated analgesia in the snail, Cepaea, and (2) that the inhibitory effects of magnetic fields on opiate-induced analgesia involve alterations in PKC.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1993

Neurophysiological correlates of tactile stimulus-induced whole-body eversion, a novel type of behavior in the snail Helix pomatia L.

Repeated weak tactile stimuli to the exposed skin of the foot of withdrawn snails (Helix pomatia L.) result in a rapid whole-body eversion response not previously described. We studied the neurophysiological correlates of this novel type of behavior in semi-intact preparations consisting of the foot, pneumostome and mantle collar attached to the CNS. The pneumostome opening component of the eversion response is retained in semi-intact preparations and can be triggered by a series of weak tactile stimuli to the foot. The same stimuli also strongly excite a giant neuron (LPd7) in the pedal ganglion. This cell has axon branches in the anal and left pallial nerve which innervate the pneumostome and mantle collar. Intracellular stimulation of LPd7 causes the pneumostome to open. Bursts of spikes in LPd7 also lead to contractions of a specific group of muscles in the mantle collar innervated by the left pallial nerve. Both responses are retained when the CNS is bathed in high Mg2+/0 Ca2+ saline but the mantle response has a much shorter latency than the opening of the pneumostome. We conclude that LPd7 is an efferent neuron which causes opening of the pneumostome via a peripheral pathway in the mantle collar and may also be a motoneuron of muscles in the mantle collar. Besides its pneumostome-opener and putative mantle motoneuron function, the LPd7 cell also triggers movements of the foot which are also part of the eversion sequence in intact snails. The LPd7 cell receives excitatory input from neurons which trigger withdrawal reactions in active snails. The excitation is due to peripheral interactions between the two cell types and leads to opening of the closed pneumostome following brief aversive stimuli. We suggest that LPd7 is part of a novel putative neuronal network underlying the described eversive reaction to tactile stimuli.

Animals↗

PubMed1993

WWamide-1, -2 and -3: novel neuromodulatory peptides isolated from ganglia of the African giant snail, Achatina fulica.

Three novel neuropeptides, isolated from ganglia of the African giant snail, Achatina fulica, were named WWamide-1, -2 and -3. These substances were biologically active heptapeptide amides with a Trp residue at both the N- and C-termini. WWamide-1, which displayed an inhibitory activity on a central neuron of the snail, exhibited peripherally modulatory effects on muscular contractions of not only the gut and other tissues of the snail but also certain tissues of other molluscs.

Amino Acid Sequence↗

PubMed1993

Lipids in the broodsac of Leucochloridium variae (Digenea, Leucochloridiidae) and its snail host Succinea ovalis.

Thin-layer chromatographic analysis was used to examine lipophilic pigments and neutral lipids in the broodsac of Leucochloridium variae and in the tissues of its snail host, Succinea ovalis. Beta-carotene and lutein were not detected in either the parasite or the host on a C-18 reversed phase layer developed in a solvent system of petroleum ether-acetonitrile-methanol (2:4:4). This chromatographic system was able to detect 10 ng of a beta-carotene standard and 100 ng of a lutein standard. The Mangold solvent system on a silica gel plate showed the presence of triacylglycerols, free sterols, and sterol esters as the major neutral lipids in both snail and parasite tissues. As seen in a previous sporocyst-snail relationship, the qualitative neutral lipid profiles of both host and parasite are similar.

Animals↗

PubMed1992

A comparative study of hemocytes from six different snails: morphology and functional aspects.

Hemocytes taken from six different gastropod snails, Achatina achatina, A. fulica, Biomphalaria glabrata, Bulinus natalensis, Helix aspersa, and Lymnaea stagnalis, were compared for morphology, peroxidase activity, and, using methods developed for L. stagnalis, the ability to generate reactive oxygen inermediates upon phagocytic stimulation. Numbers of hemocytes per milliliter hemolymph and hemocytes' microscopical morphology showed some variation among the snail species. Peroxidase activity was demonstrated in all snail hemocytes except in those of B. glabrata and A. fulica. Hemocytes of all species generated superoxide upon phagocytic stimulation with zymosan (tested by superoxide dismutase-inhibitable reduction of nitroblue tetrazolium). When tested, hemocytes of A. achatina and of A. fulica displayed luminol-dependent chemiluminescence activity.

Animals↗

PubMed1983

Tolerance to the morphine-influenced thermal response in the terrestrial snail, Cepea nemoralis.

The terrestrial snail, Cepea nemoralis, displayed stereotyped thermal-avoidance behavior, with morphine increasing and naloxone decreasing the latency of this response. After 5-7 days of daily administration of morphine sulfate (1 microliter of 0.10-10.0 mg/ml) the thermal responses of snails displayed tolerance to morphine. The response latency was reduced to that of saline-treated individuals. Pretreatment with the protein synthesis inhibitor, cycloheximide, blocked the development of tolerance. After termination of chronic treatment with morphine, tolerant snails exhibited withdrawal signs that included increased responsiveness to naloxone, decreased responsiveness to morphine and saline and behavioral alterations suggesting irritation and hyperactivity. These results suggest that the thermally-induced behavior of Cepea can serve as a useful model for the investigation of the development of opioid tolerance and physical dependence in mammals.

Animals↗

PubMed1984

The presence of an opioid system mediating behavioral thermoregulation in the terrestrial snail, Cepaea nemoralis.

Administration of the opiate agonist, morphine sulfate (0.1-10 micrograms per snail) resulted in a significant dose- and time-dependent increase in the temperatures selected by the terrestrial snail, Cepaea nemoralis, in a thermal gradient. These thermoregulatory effects could be blocked and reversed by naloxone hydrochloride, with the opiate antagonist by itself (1 and 10 micrograms) causing a significant decrease in preferred temperatures. After 6-10 days of daily administration of morphine, Cepaea displayed tolerance, the effects of morphine decreasing and thermal preferences becoming similar to those of saline-treated individuals. These results suggest that an opioid system is involved in the control of thermoregulation in snails, in a manner that is similar to that shown by vertebrates.

Animals↗

PubMed1985

The effects of opioid and FMRF-amide peptides on thermal behavior in the snail.

Administration of methionine-enkephalin, beta-endorphin or, as previously shown, the opiate agonist, morphine sulfate (0.10-10.0 micrograms per snail), resulted in significant dose-dependent increases in the latency of thermal (40 degrees C hot plate) avoidance behavior of the terrestrial snail, Cepaea nemoralis. The analgesic effects could be blocked by the opiate antagonist, naloxone, as well as by the non-opioid peptides, FMRF-amide and YGG-FMRF-amide. When administered by themselves the FMRF-amide peptides had significant bimodal effects either decreasing (0.10 and 10.0 micrograms) or increasing (1.0 micrograms) the latency of the response to the thermal stimulus. These results indicate that opioid and FMRE-amide peptides may be involved in the determination of thermal behavior in the snail. They also suggest that FMRF-amide peptides may function as endogenous modulators of opioid activity.

Animals↗

PubMed1994

Central chemoreceptor stimulus in the terrestrial, pulmonate snail, Helix aspersa.

We studied the effect of hypercapnic and fixed acid central chemoreceptor stimulation on the pneumostome in the pulmonate snail, Helix aspersa. We found that focal stimulation of the central chemoreceptor area of the pulmonate snail brain with hypercapnic solutions more effectively increased the pneumostomal area than did fixed acid stimulation at the same extracellular pH. Disrupting intracellular pH regulation by inhibiting Cl- transport, either pharmacologically (DIDS) or by ion substitution (Cl(-)-free perfusate), enhanced pneumostomal responses to CO2. While maintaining a constant perfusate pH, addition of NH4Cl to the perfusate resulted in pneumostomal closure; whereas removal of NH4Cl from the bath resulted in pneumostomal opening. In conclusion, the ventilatory response to CO2 in H. aspersa does not require Cl- transport or conductance. Furthermore, changing pHi alone is an adequate stimulus for the central chemoreceptors in the snail.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1993

CELSS nutrition system utilizing snails.

At the 40th IAF Congress in Malaga, a nutrition system for a lunar base CELSS was presented. A lunar base with a total of eight crew members was envisaged. In this paper, four species of plants--rice, soybean, lettuce and strawberry--were introduced to the system. These plants were sufficient to satisfy fundamental nutritional needs of the crew members. The supply of nutrition from plants and the human nutritional requirements could almost be balanced. Our study revealed that the necessary plant cultivation area per crew member would be nearly 40 m3 in the lunar base. The sources of nutrition considered in the study were energy, sugar, fat, amino acids, inorganic salt and vitamins; however, calcium, vitamin B2, vitamin A and sodium were found to be lacking. Therefore, a subsystem to supply these elements is of considerable value. In this paper, we report on a study for breeding snails and utilizing meat as food. Nutrients supplied from snails are shown to compensate for the above mentioned lacking elements. We evaluate the snail breeder and the associated food supply system as a subsystem of closed ecological life support system.

Animals↗